Rock bolt

Abstract

A rock bolt (1) has a tubular body (2) with first and second ends (3, 4). The first end (3) is substantially sealed. A threaded rod (5) extends from the tubular body second end (4) for receiving a nut 102. A portion (6) of the tubular body (2) at the second end (4) is crimped on to the threaded rod (5). A rock bolt assembly is also disclosed comprising a rock bolt (1), a sleeve (105) coaxially mounted oil the rock bolt (1), a resin cartridge (104) received in the sleeve (105) and a collar (107) mounted on the leading end (106) of the sleeve (105) to engage a rock face and prevent the sleeve (105) from entering a hole in the rock face into which the rock bolt (1) is installed.

Description

FIELD OF THE INVENTION

[0001] The present invention relates to mining equipment, and in particular relates to a rock bolt for securing the roof of a mine.

BACKGROUND OF THE INVENTION

[0002] A known method of installing a resin grouted rock bolt to secure the roof of an underground mine involves drilling a hole to accommodate the bolt and inserting a container of resin into the hole. The bolt is then driven into the hole to puncture the walls of the resin container and mix the resin to secure the bolt in the hole once the resin has set.

[0003] Due to the nature of the resin being generally used, the clearance between the outer diameter of the bolt and the diameter of the hole has to be minimised to ensure proper mixing of the resin. Typically, the annulus should not be larger than 3 mm. In coal mining, the annulus varies between 1.75 mm and 2.0 mm where standard 22 mm diameter bolts are used.

[0004] However, holes currently being drilled for bolt installation in hard rock mining are larger as compared to those of coal mining. The annulus in hard rock mining can vary from 5 mm to 11 mm. Therefore, in hard rock mining, a standard 22 mm diameter rock bolt cannot be used as a resin grouted anchor because the resin does not mix properly in the larger annulus. In hard rock mining, it is not generally practical to drill smaller holes due to limitations of the type of drilling equipment in general use. That is, the annulus can generally only be reduced by using a suitable bolt.

[0005] Reduction of the annulus by use of a solid bolt of a larger diameter is not economical and is often impractical. Therefore, to improve the mixability of the resin, specifically modified bolts have been prepared, with varying levels of success.

[0006] When resin cartridge is inserted into a hole prior to insertion of a rock bolt, the resin cartridge can readily fall from the hole prior to insertion of the bolt. Accordingly, resin cartridges are typically inserted into the hole at the same time as the rock bolt, with the resin cartridge being pushed into the hole by the upper end of the rock bolt. To facilitate this process, a sleeve is often mounted on the upper end of the rock bolt so as to extend therefrom, providing a cavity within which the resin cartridge can be mounted. The rock bolt assembly incorporating the bolt sleeve and resin cartridge can then be readily inserted into the rock bolt hole. The sleeve, however, becomes lodged within the hole and provides a barrier preventing full encapsulation of the rock bolt in resin.

OBJECT OF THE INVENTION

[0007] It is the object of the present invention to provide an improved rock bolt and rock bolt assembly and/or at least an effective alternative to current rock bolts and rock bolt assemblies.

SUMMARY OF THE INVENTION

[0008] In one broad form the present invention provides a rock bolt comprising:

[0009] a tubular body having first and second ends, said tubular body first end being substantially sealed; and

[0010] a threaded rod extending from said tubular body second end for receiving a nut;

[0011] wherein a portion of said tubular body at said second end is crimped onto said threaded rod.

[0012] Preferably, said crimped portion of said tubular body has a length of at least 100 mm.

[0013] Preferably, said threaded rod is provided with an enlarged head, said enlarged head being disposed within said tubular body.

[0014] Preferably, said enlarged head is located a distance from a shoulder defined by the junction between said crimped portion of said tubular body and an adjacent uncrimped portion thereof.

[0015] Preferably, said crimped portion of said tubular body is configured such that said threaded rod is displaced relative to said crimped portion upon application of a predetermined tensile load less than the ultimate tensile strength of said tubular body and of said threaded rod.

[0016] Preferably, said predetermined tensile load is in excess of 90% of the lesser of said tubular body ultimate tensile strength and said threaded rod ultimate tensile strength.

[0017] Preferably said tubular body first end is crimped.

[0018] Preferably, said exterior surface of said tubular body is provided with generally helical deformations.

[0019] A second threaded rod may extend from said tubular body first end for receiving an expansion shell.

[0020] In another broad form the present invention provides a rock bolt assembly comprising:

[0021] a rock bolt having first and second ends, said rock bolt having a threaded portion at said second end;

[0022] a sleeve having leading and trailing ends and being coaxially mounted on said rock bolt with said leading end extending beyond said rock bolt first end to define a cavity;

[0023] a resin cartridge received in said cavity; and

[0024] a first detent means associated with said sleeve leading end adapted to engage a rock face about a hole in which said rock bolt is to be installed to thereby prevent said sleeve from entering said hole.

[0025] Preferably, said first detent means is in the form of a first collar coaxially mounted on said resin cartridge adjacent said sleeve leading end, said collar having a leading face adapted to engage said rock surface and a trailing face adapted to engage said sleeve leading end.

[0026] Preferably, said sleeve is readily destructable.

[0027] Preferably, said rock bolt assembly further comprises a second detent means adapted to engage said sleeve trailing end on installation of said rock bolt into said hole and compress and/or tear said sleeve between said first and second detent means.

[0028] Preferably, said second detent means is in the form of a second collar coaxially mounted on said bolt towards said second end thereof, said second collar having a leading face adapted to engage said sleeve trailing end and a trailing face adapted to engage a nut threaded onto said rock bolt threaded portion.

[0029] Preferably, said first collar trailing face and/or said second collar leading face is provided with an annular tapered surface adapted to tear said sleeve upon engagement therewith.

[0030] Preferably, said sleeve is formed of cardboard material.

BRIEF DESCRIPTION OF THE DRAWINGS

[0031] A preferred form of the present invention will now be described by way of example with reference to the accompanying drawings, wherein:

[0032] FIG. 1 is a fragmentary cross-sectional side elevation view of a tubular rock bolt installed in a rock roof;

[0033] FIG. 2 is a fragmentary cross-sectional side elevation view of an alternate tubular rock bolt installed in a rock roof;

[0034] FIG. 3 is a fragmentary cross-sectional side elevation view of a further alternate tubular rock bolt installed in a rock roof,

[0035] FIG. 4 is a fragmentary partially cross-sectioned side elevation view of a rock bolt assembly; and

[0036] FIG. 5 is a fragmentary cross-sectional side elevation view of the upper portion of a further tubular rock bolt installed in a rock roof.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0037] With reference to FIG. 1, a rock bolt 1 comprises a tubular body 2 having first and second ends 3, 4. A threaded rod 5 extends from the tubular body second end 4. A portion 6 of the tubular body 2 at the second end 4 thereof is crimped onto the threaded rod 5 so as to fix the threaded rod 5 to the tubular body 2 and enable the transfer of loads, particularly tensile loads, between the two components of the rock bolt 1.

[0038] The tensile load able to be transferred between the threaded rod 5 and crimped portion 6 of the tubular body 2 will be likely determined by the length of the crimped portion 6 and the crimping force applied. Typically, the crimped portion will have a length of 100-200 mm to enable sufficient load transfer.

[0039] To improve the tensile load transfer capabilities between the threaded rod 5 and tubular body 2, the threaded rod 5 may be provided with an enlarged head 7 which is disposed at the end of the threaded rod 5 within the tubular body 2, as depicted in FIGS. 2 and 3. The enlarged head 7 may be provided by flattening of the rod end or by any other known means such as by screw threading the head 7 onto the rod 5. The crimping of the crimped portion 6 about the threaded rod 5 provides an annular shoulder 8 within the tubular body 2 at the junction of the crimped portion 6 and the adjacent uncrimped portion. In the rock bolt configuration depicted in FIG. 2, the enlarged head 7 bears against the shoulder 8. When a tensile load is imparted on the threaded rod 5, much of this load can effectively be transferred to the tubular body 2 via the bearing of the enlarged head 7 on the tubular body shoulder 8. This load transfer reduces the length of the crimped portion 6 required to provide an effective tensile load transfer during tensioning of the rock bolt and service loads encountered in supporting the rock.

[0040] In the rock bolt configuration depicted in FIG. 3, the enlarged head 7 is located a distance from the shoulder 8. With this configuration, rock burst conditions can be effectively contained. Upon the occurrence of a rock burst, which results in a sudden large tensile load being applied to the rock bolt, the crimped portion 6 can be configured such that the crimped connection between the crimped portion 6 and the threaded rod 5 fails such that the threaded rod 5 will be displaced relative to the crimped portion 6, effectively pulling the threaded rod 5 out of the tubular body 2. Such displacement will continue until the enlarged head 7 comes into contact with the shoulder 8. Engagement between the enlarged head 7 and shoulder 8 prevents further displacement of the threaded rod 5 and enables the tensile load to be carried by the rock bolt 1. This configuration can thus be seen to allow the rock bolt 1 to effectively yield under rock burst conditions and allow the immediate rock mass to move some distance to dissipate the kinetic energy within the rock whilst eventually stopping the rock movement and preventing the failure of the rock containment. The yieldability of the bolt will be controlled by the length of the crimped portion 6 and the crimping force used to secure the tubular body 2 to the threaded rod 5. The force at which the crimping connection will fail should be less than the ultimate tensile strength of the tubular body 2 and of the threaded rod 5. The crimp failure load should preferably be in excess of 90% of the lesser of the ultimate tensile strength of the tubular body 2 and of the threaded rod 5 such that only excessive loads will result in yielding of the bolt.

[0041] A degree of yieldability of the rock bolt will also be exhibited if the enlarged head 7 is omitted, and the threaded rod 5 still extends into the tubular body 2 beyond the crimped portion 6. Small relative movements between the threaded rod 5 and the crimped portion 6 will still result in the threaded rod 5 engaging the crimped portion 6 along the entire length of the crimped portion 6.

[0042] The tubular body first end 3 is at least substantially sealed to prevent the ingress of resin into the interior of the tubular body 2. This sealing can effectively be provided by crimping of the tubular body first end 3.

[0043] The exterior surface of the tubular body 2 is here provided with deformations 9 of a generally helical configuration which are rolled into the steel tubular body.

[0044] The rock bolt 1 is particularly suitable for use in securing the roofs of hard rock mines which typically have enlarged roof holes drilled as compared to coal mines, as discussed above. For a typical 45 mm diameter hole in hard rock, the tubular body will typically have a diameter of approximately 39 mm allowing for a small annular gap of approximately 3 mm width.

[0045] The rock bolt 1 will typically be installed utilising a chemical anchor to secure the first end 3 thereof. Whilst the rock bolt 1 can be installed utilising a resin cartridge to provide a chemical anchor in the usual manner, a preferred rock bolt assembly mounting a resin cartridge 104 on the rock bolt tubular body first end 3 is depicted in FIG. 4. In this rock bolt assembly, a sleeve 105 having leading and trailing ends 106, 107 is coaxially mounted on the rock bolt 1 with the leading end 106 extending beyond the tubular body first end 3. A resin cartridge 104 is received in the cavity defined in the portion of the sleeve 105 extending beyond the tubular body first end 3. A first detent means, here in the form of a first collar 108, is associated with the sleeve leading end 106 and is sized such that, as depicted in FIG. 3, it engages the rock face about a hole 100 in which the rock bolt is to be installed, thereby preventing the sleeve 105 from entering the hole. The first collar 108 is formed of plastic material and has a cylindrical tail portion 109 which fits inside the sleeve 105 and is mounted on the resin cartridge 104. The first collar 108 has a leading face 110 which engages the rock face and a tapered trailing face 111 which engages the sleeve leading end 106.

[0046] The sleeve 105 is here formed of a readily destructible material, and in particular cardboard, such that it can be readily compressed or torn during installation, as will be described below. To assist in this regard, a second detent means in the form of a steel second collar 112 is provided on the threaded rod 5 of the rock bolt 1. The second collar 112 has a tapered leading face 113 which engages the sleeve trailing end 107 and a trailing face 114 which engages the nut 102 threaded on to the threaded rod 5. The second collar 112 also engages the mine/roof plate 103. Alternatively, the rock bolt 1 can be configured such that the nut or roof plate forms the second detent means engaging the sleeve trailing end 107.

[0047] A tapered plastic cap 115 is mounted on to the leading end of the resin cartridge 104 to protect the cartridge 104 against sharp protrusions and to enable easier insertion of the rock bolt assembly into the hole 100.

[0048] During installation, a hole 100 is first drilled in the mine roof in the usual manner. The rock bolt assembly is then pushed into the hole with the plastic cap 115 leading. When the first collar 108 reaches the entrance to the hole, the first collar leading face 110 engages the rock face about the hole, preventing the sleeve 105 from entering the hole. As the rock bolt assembly is further pushed into the hole, the resin cartridge 104 is effectively extruded through the sleeve 105 as it is continued to be pushed by the rock bolt 1 whilst the sleeve 105 is held back from the hole. Once the resin cartridge 104 is entirely within the hole, there is no further need for support by the sleeve 105, with the rock bolt 1 continuing to push the resin cartridge 104 toward the top of the hole 100.

[0049] As the rock bolt 1 extends through the now stationary sleeve 105 the tapered leading face 113 of the second collar 112 comes into engagement with the sleeve trailing end 107. Further advancement of the rock bolt 1 results in both the second collar leading tapered face 113 and the first collar trailing tapered face 111 forcibly engaging the ends of the sleeve 105. This force applied to the ends of the sleeve 105 causes the sleeve to ride up over the tapered surfaces 111, 113 of the collars 108, 112, resulting in the cardboard material of the sleeve 105 being tom, thereby destroying the sleeve. It is also envisaged that the detent means might alternately be arranged such that the cardboard sleeve is merely compressed and crushed between the detent means.

[0050] As the rock bolt 1 is still further advanced, the second collar 112 engages the cylindrical tail 109 of the first collar and squashes the same. The advancement of the second collar 112 is restrained by the roof plate 103 bearing against the rock face. The amount by which the first collar tail 109 is crushed is accordingly largely dependent upon the space available between the roof plate 103 and the rock face, as depicted in FIG. 3. The destroyed cardboard sleeve 105 is also largely housed within the cavity defined between the roof plate 103 and the rock face although some shreds of cardboard may pull away from the assembly.

[0051] Once the resin cartridge 104 reaches the top of the hole, it is punctured by the tubular body first end 3 of the rock bolt 1.

[0052] The resin 101 is then mixed by rotation of the rock bolt 1, typically by rotation of the nut 102. The crimping of the tubular body first end 3 provides a flattened end portion which assists in the mixing of the resin. The helix deformations 9 formed in the exterior surface of the tubular body 2 act to pump the resin 101 toward the tubular body first end 3, assisting in the prevention of voids in the resin 101. The helical deformations 9 also provide an improved bond between the tubular body 2 and the resin 101 by way of a keying type effect.

[0053] By ensuring that the cardboard sleeve 105, which would typically have a length of the order of 1 metre as compared to the total bolt length of 2.4 metres, does not enter the hole 100, encapsulation of the bottom half of the bolt 1 in resin is not impeded. Full encapsulation provides a more effective and secure installation of the bolt enabling load transfer over the full length of the bolt 1. Whilst it is preferred that the sleeve 105 is destroyed during installation, it is envisaged that the rock bolt assembly might be arranged such that the sleeve 105 is merely ejected from the rear of the bolt during installation.

[0054] After the resin has cured, the nut 102 and roof plate 103 assembly is tightened onto the threaded rod 5, imparting a tensile stress on the rock bolt 1 which is transferred from the threaded rod 5 to the tubular body 2 via the crimped portion 6. Tensioning of the bolt applies a compressive load which consolidates the roof material.

[0055] The sleeve and detent means arrangement described above could equally be applied to various forms of rock bolt other than the specific tubular rock bolt 1 described above.

[0056] Where it is desired to utilise a known expansion shell, comprising a wedge and leaves, in addition to the resin cartridge to assist in anchoring the rock bolt, a second threaded rod 10 may be extended from the tubular body first end 3 for receipt of the expansion shell 200, as depicted in FIG. 5. In such a configuration, the second threaded rod 10 would typically be secured to the tubular body 2 by crimping the tubular body first end onto the second threaded rod 10.

[0057] Other possible modifications will be apparent to the person skilled in the art.

Claims

1. A rock bolt comprising:

a tubular body having first and second ends, said tubular body first end being substantially sealed; and

a threaded rod extending from said tubular body second end for receiving a nut;

wherein a portion of said tubular body at said second end is crimped onto said threaded rod.

2. The rock bolt of claim 1 wherein said crimped portion of said tubular body has a length of at least 100 mm.

3. The rock bolt of either of claims 1 and 2 wherein said threaded rod extends into said tubular body beyond said crimped portion.

4. The rock bolt of any one of claims 1 to 3 wherein said threaded rod is provided with an enlarged head, said enlarged head being disposed within said tubular body.

5. The rock bolt of claim 4, when appended to claim 3, wherein said enlarged head is located a distance from a shoulder defined by the junction between said crimped portion of said tubular body and an adjacent uncrimped portion thereof.

6. The rock bolt of either of claims 3 and 5 wherein said crimped portion of said tubular body is configured such that said threaded rod is displaced relative to said crimped portion upon application of a predetermined tensile load less than the ultimate tensile strength of said tubular body and of said threaded rod.

7. The rock bolt of claim 6 wherein said predetermined tensile load is in excess of 90% of the lesser of said tubular body ultimate tensile strength and said threaded rod ultimate tensile strength.

8. The rock bolt of anyone of claims 1 to 7 wherein said tubular body first end is crimped.

9. The rock bolt of anyone of claims 1 to 8 wherein said exterior surface of said tubular body is provided with generally helical deformations.

10. The rock bolt of anyone of claims 1 to 9 wherein a second threaded rod extends from said tubular body first end for receiving an expansion shell.

11. A rock bolt assembly comprising:

a rock bolt having first and second ends, said rock bolt having a threaded portion at said second end;

a sleeve having leading and trailing ends and being coaxially mounted on said rock bolt with said leading end extending beyond said rock bolt first end to define a cavity;

a resin cartridge received in said cavity; and

a first detent means associated with said sleeve leading end adapted to engage a rock face about a hole in which said rock bolt is to be installed to thereby prevent said sleeve from entering said hole.

12. The rock bolt assembly of claim 11 wherein said first detent means is in the form of a first collar coaxially mounted on said resin cartridge adjacent said sleeve leading end, said collar having a leading face adapted to engage said rock surface and a trailing face adapted to engage said sleeve leading end.

13. The rock bolt assembly of either of claims 11 and 12 wherein said sleeve is readily destructible.

14. The rock bolt assembly of claim 13 further comprising a second detent means adapted to engage said sleeve trailing end on installation of said rock bolt into said hole and compress and/or tear said sleeve between said first and second detent means;

15. The rock bolt assembly of claim 14 wherein said second detent means is in the form of a second collar coaxially mounted on said bolt towards said second end thereof, said second collar having a leading face adapted to engage said sleeve trailing end and a trailing face adapted to engage a nut threaded onto said rock bolt threaded portion.

16. The rock bolt assembly of anyone of claims 13 to 15 wherein said first collar trailing face is provided with an annular tapered surface adapted to tear said sleeve upon engagement therewith.

17. The rock bolt assembly of claim 15 wherein said second collar, leading face is provided with an annular tapered surface adapted to tear said sleeve upon engagement therewith.

18. The rock bolt assembly of any one of claims 11 to 17 wherein said sleeve is formed of cardboard material.

19. A rock bolt substantially as hereinbefore described with reference to any one of FIGS. 1 to 3 or 5.

20. A rock bolt assembly substantially as hereinbefore described with reference to FIG. 4.